Method for producing bulk ceramic components from agglomerations of partially cured gelatinous polymer ceramic precursor resin droplets

ABSTRACT

Methods, processes, and systems for producing bulk ceramics from agglomerations of partially cured gelatinous polymer ceramic precursor resin droplets, without using sponge materials to form gas pathways in the polymer bodies. Ceramics can be formed in hours. Resin droplets can be produced with a sprayer where liquid polymer precursors, mixed with a curing agent, are sprayed forming droplets which are partially cured, collected, and compressed into shapes. Ceramic porosity can be varied, droplet particle sizes can be controlled by adjusting liquid and gas pressure, orifice size, during spraying. Partially cured droplets can be formed via an emulsion process and size controlled by emulsion liquid and surfactant selection parameters.

CROSS REFERENCE TO RELATED APPLICATIONS

This invention claims the benefit of priority to U.S. ProvisionalApplication Ser. No. 61/606,007 filed Mar. 2, 2012, the entiredisclosure which is incorporated herein by specific reference thereto.

FIELD OF INVENTION

This invention relates to bulk ceramic components, and in particular tomethods, processes, and systems for producing bulk ceramic componentsfrom agglomerations of partially cured gelatinous polymer ceramicprecursor resin droplets and methods of use thereof.

BACKGROUND AND PRIOR ART

There are several processes to manufacture bulk ceramic components fromdifferent ceramic materials. The processes have in common that theceramic material can be made into shapes with thick cross sections,which is opposed to thin film ceramics that are sprayed onto a substrateand then fired into a ceramic coating.

A majority of ceramic materials are made by mixing powdered ceramicmaterials with various liquids to create a slurry that can be injectedor poured into a mold and then dried like plaster or concrete. The driedliquid acts as a binder that temporarily holds the ceramic powderparticles in place and together. The dried, molded shapes are thenplaced in a furnace at high temperature, the dried liquid binder isburned out, and the ceramic powder particles begin to fuse together in asolid-state diffusion process.

The particles do not melt but are essentially “welded” together whereverthey make contact with each other. Since the particles do not melt,there is space between them when the sintering process is complete. Thisspace gives rise to a final product that is porous. The amount and sizeof the pores depend on the size of the ceramic particles.

Another route to obtaining ceramic material does not involve ceramicpowders. This route involves liquid polymer resins that are cured to asolid and then fired in a furnace where the polymer material isconverted through chemical transformations into a ceramic material. Thisclass of ceramic is known as Polymer Derived Ceramics (PDC's).

The problem with PDC's is that as they convert to a ceramic under hightemperature, they go through extensive shrinking and there is asubstantial mass loss that is manifested in the form of gas evolution.Typically, if the cross section of the cured polymer is too large thegas generated inside the solid during the ceramic transformation causesa pressure build up that will crack the polymer body and result in aceramic part with multiple cracks. To avoid the formation of cracksduring the ceramic transformation the evolving gas needs to diffusethrough the solid polymer phase and out to the surface. The longer thepathway leading to the surface the more diffusion resistance there isand the greater the internal backpressure. Therefore, there is a maximumdiffusion length that can be tolerated in a pre-ceramic polymer shape.Because of this, PDC's were typically used for thin film coatings andmicro-scale component applications.

The inventor was a co-inventor on U.S. patent application Ser. No.13/372,297, now U.S. Pat. No. 8,119,057 which issued Feb. 21, 2012,which is incorporated by reference. The patent covered the method forsynthesizing bulk ceramics and structures from polymeric ceramicprecursors, and required the use of open cell material to form ceramicstructures, where the liquid ceramic precursors were poured into aplastic sponge material and then solidified. The resulting solid polymerblock with the plastic sponge inside could then be machined into anyshape then placed into a furnace and converted to ceramic. The key herewas that the sponge would melt and or burn out at a low temperature andleave a connected network of internal passageways that would allow thegases to escape as the polymer converted to a ceramic. As long as theinternal gasses did not have to diffuse through the solid parts morethan the critical distance before encountering one of the internal openpassageways, the internal pressure would not get high enough to causecracks. Currently, this is the only method known for bulk ceramic partsto be made with these polymer derived ceramics.

However, there are drawbacks to this method. The critical diffusionlength of these polymer precursors is fairly small, about 50 microns orless and therefore a sponge material has to be chosen that has pores of50 microns or less. There are not many sources of such materials.Another requirement of the sponge material is that it must decompose ata temperature lower than the temperature at which the polymer precursorsstart to convert to ceramic and produce gas. This temperature is quitelow, about 300 C and there are not many sponge materials that have thepore structure and thermal decomposition properties required for thisceramic producing process. Another major drawback of this method is thatit takes a long time to burn out this sponge material. If the part hasthick cross sections it can take days or even weeks to completely burnout the sponge material before the temperature can be increase into theceramic production range.

Thus, the need exists for solutions to the above problems with the priorart.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components fromagglomerations of partially cured gelatinous polymer ceramic precursorresin droplets.

A secondary objective of the present invention is to provide methods,processes, and systems for producing unique morphologies in bulk ceramiccomponents.

A third objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components withoutusing sponge materials to produce gas pathways in the polymer bodies.

A fourth objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components in hoursinstead of days and weeks.

A fifth objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components with asprayer where liquid polymer precursors, mixed with a curing agent, aresprayed to form droplets which are partially cured, collected, andcompressed into a shape form.

A sixth objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components whereceramic porosity can be varied from 25%-98%.

A seventh objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components with aspraying process, where droplet size of particles can be controlled byadjusting liquid pressure and gas pressure and orifice size as well asother parameters during the spraying process.

An eighth objective of the present invention is to provide methods,processes, and systems for producing bulk ceramic components with aspraying process using liquid droplets, where percentage of full cure ofthe liquid droplets can be controlled by the curing agent used, thecuring temperature, and the time at that temperature.

Further objects and advantages of this invention will be apparent fromthe following detailed description of the presently preferredembodiments which are illustrated schematically in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flowchart showing the steps of using resin to form ceramiccomponents.

FIG. 2 shows the steps of creating plumbing with bulk ceramiccomponents.

FIG. 3 shows the steps for creating conductor networks with bulk ceramiccomponents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining the disclosed embodiments of the present invention indetail it is to be understood that the invention is not limited in itsapplications to the details of the particular arrangements shown sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

This new invention disposes of the sponge material completely and usesan entirely different method to produce the necessary gas pathways inthe polymer body. Without the need to burn out a sponge material,ceramic parts of very large cross section can be produced in a matter ofhours instead of days or weeks.

This new method of making pre-ceramic bulk parts with the required gaspathways uses a spraying technique where the liquid polymer precursors,which have been mixed with a curing agent, are sprayed eitherhydraulically or with gas assist to form droplets which are thenpartially cured and then collected, while still sticky or tacky, andthen compressed into a mold or put through some other shape producingstep.

It is important that the droplets not be 100% cured because they willnot be able to form chemical bonds to each other which means they willnot convert to a single continuous ceramic body. Instead each dropletwould convert to a small droplet sized ceramic granule and theagglomeration would fall apart. The amount of compression has to becontrolled so as not to squeeze all of the air out which would mean thegas path ways have been squeezed shut, which will lead to pressure buildup, and part failure during firing.

In a paper published in “The Journal of the American Ceramics Society”by Hans-Joachim Kleebe (“Decomposition-Crystallization ofPolymer-Derived Si—C—N Ceramics) J. Am. Ceram. Soc., 81 [11} 2971-77(1998)) Kleebe describes a process where a sample of a polymer ceramicprecursor was cured to a solid then crushed into a powder. Then moreliquid precursor was mixed in to form a slurry which was then pressedinto disks.

The resulting ceramic has some residual porosity due to trapped air andfrom shrinkage of the liquid as it cures to a solid. The pores howeverare non-uniform in size or spacing. Because a liquid was mixed with apowder, there was essentially no uniform network of gas pathways formedand therefore ceramic components with cross sections larger then 1 mmwould not be possible.

The partially cured particles in the method proposed here are semi solidwith a tacky surface. The spherical semi solid droplets hold their shapeand thus maintain open pathways between them when they are in contact.By applying pressure to a collection of these semi solid spheres, thesize of the gas pathways can be reduced to any desired level as long asthey are not reduced to zero by over compression of the spheres.

Because the spheres are only partially cured and they are still sticky,the collections of spheres will hold together and can be molded likeclay into any shape or they can be pressed into a mold. By varying theamount of compression in different areas of a part made in this way onecan produce final ceramic parts with density that varies in acontrollable way from one end of the part to the other.

Additionally, if a non-porous, fully dense surface is desired, the spacebetween the semi solid spheres (beads) on and near the surface can beclosed off by applying extra beads and/or applying localized mechanicalpressure such that the surface beads are smeared, spackled or otherwiseforced into the open pores of the surface being sealed.

Once the green body is cured and pyrolyzed the resulting bulk ceramiccomponent will have a fully dense, non-porous surface suitable forpolishing, metalizing or any number of additional surface treatments.

Because the spheres are only partially cured, the molded part can thenbe placed in an oven to complete the cure. After full curing theindividual spheres are chemically bonded together and when fired willproduce a single continuous ceramic part where the previous individualspheres are indistinguishable.

Advantages of making ceramic components with this method are: Ceramicporosity can be varied from 2% to 98%.

By adjusting liquid pressure and gas pressure and orifice size as wellas other parameters during spraying, the droplet size can be controlled.

The percentage of full cure of the liquid droplets can be controlled bythe curing agent used, the curing temperature, and the time at thattemperature.

In one embodiment of the invention described in reference to FIG. 1, theliquid polymer ceramic precursor resins can be sprayed into a curingchamber of hot gas (air, nitrogen, argon, and the like) where the gastemperature is adjustable and the droplets would descend under gravitythrough the chamber which can be varied in height to control the timespent by the droplets in the hot zone which controls the amount of cure.

The partially cured spherical droplets would then fall into a funnel andcollected.

An alternative to hot gas cure, with the appropriate curing agent, thecuring chamber could be flooded with radiation (IR (infra red), UV(ultra violet), Microwave, and the like).

Yet another way to partially cure and collect the droplets would be tospray them into a hot, non-reactive, immiscible, liquid bath. This wouldform an emulsion to which a surfactant may be added to stabilize theemulsion while the liquid droplets cure. The emulsion could also beformed by pouring the liquid resin into the hot curing liquid thenmixing with a high shear method to produce small droplets of resin inthe emulsion. The droplets would then be scooped out and the excessliquid removed by squeezing or spinning before the final cure. Theamount of initial cure can vary from >0-<100%.

Another major advantage of this process is that multiple differentceramic precursors can be co-sprayed in different ratios to produce afinal composite ceramic body that would be made up of multiple differentceramics bonded together in a uniformly distributed pattern.

If desired the pre-ceramic resins could be co-sprayed with an inertfiller that would burn out during firing. This would allow the spheresto be highly compacted without completely closing up the space betweenthem. If desired the inert filler could be a metal powder where themetal would melt/sinter together and form a metal ceramic composite thatcould be made quickly and easily and with very uniform properties.

FIG. 1 is a flowchart showing the steps of using resin to form ceramiccomponents. One or more Polymer Derived Ceramics (PDC's) resins 5 can besprayed into a curing chamber 10. There are commercially availableresins that are precursors to SiC, SiOC, SiCN and Si3N4 ceramics amongothers.

PDC resins can include but are not limited to Polysiloxanes,polysilazanes, polyborosiloxanes, polycarbosiloxanes, polyborosilanesand polycarbosilanes.

Varying spray parameters can allow for the size and quantity of thedroplets to be controlled.

Spray parameters include but are not limited to controlling the physicalproperties of the resin such as viscosity and surface tension andcontrolling external spray parameters such as resin temperature andpressure and selection of spray nozzle geometry. For example byincreasing the pressure and reducing the diameter of the spray nozzlewill lead to smaller diameter droplets. Conversely increasing thediameter of the spray nozzle leads to larger diameter droplets. Anincrease in spray pressure typically leads to higher volume productionof droplets as well. Similarly, increasing resin temperature and orreducing viscosity or surface tension will lead to smaller dropletformation.

The size of the droplets can include but are not limited to a range ofapproximately 1 micron in size to approximately 300 microns in size.Volume quantities can be controlled by spray parameters and number ofspray nozzles and can range from a few milliliters per minute tomultiple liters per second.

The curing chamber 10 can contain heated gas or applied heat or can beflooded with electromagnetic radiation (UV, microwave, and the like) tocure the gel droplets to the desired level.

The heated gas can include but is not limited to air, nitrogen, argonetc. heated to temperature of approximately 25 C to approximately 500 Cdegrees.

Electromagnetic wavelength can include but is not limited to infrared,ultraviolet or microwaves. The cure time can be milliseconds to minutesdepending on droplet size, radiation intensity and flight time.

Optionally, the liquid PDC resins 15 can be mixed with surfactants andan inert liquid to form an emulsion of PDC resin droplets.

Surfactants can include but are not limited to PEG-12 Dimethicone,Glyceryl laurate, Polyethoxylated tallow amine, and the like.

Inert liquid can include but is not limited to Water, ethylene glycol,propylene glycol, glycerin, and the like.

The emulsion can then be heated in a mixing/heating chamber 20 topartially cure the resin droplets to the desired level.

The type of mixing chamber can include but is not limited to a stirredvat for batch production or flowing stream for continuous production.

The heating temperature can be approximately 25 C to approximately 400 Cdepending on emulsion fluid and time of heating can be seconds tominutes depending on quantity and type of crosslinking agent.

Heated liquid stirring bath can produce emulsions of PDC liquid resins.Adjusting stirring speeds, liquids in the bath and surfactants usedallows the size and quantity of gelled droplets to be controlled.Adjusting time in and temperature of the liquid bath allows control overthe percentage of cure of the gel droplets.

Stirring of the bath can produce a shear in the liquid which in turnbreaks up the liquid resin droplets into smaller units. Ultrasonicenergy can also be employed to agitate the bath. The use of ultrasonicemulsification can produce liquid droplets that are <1 micron in size.As the size of the droplets decreases the amount of surface area of theliquid resin goes up. This allows the resin to be cured at a fasterrate. Increasing the bath temperature also increases the cure rate ofthe resin. By adjusting these parameters cure times can range fromseconds to hours.

The partially cured gel droplets can be collected in a dry pan orcooling bath 30. Once the gel droplets are cured to the desired andselected level they are cooled which stops the curing process. They canbe cooled by screening them out of the heated emulsion bath and placedin a cooling bath or spread onto cool surface.

The collected partially cured gel droplets can be pressed into a mold 40which may or may not be heated to complete the cure of the gel droplets.The amount of compression can be varied which allows control over theporosity and density of the resulting green body.

Typically the cure can be completed in minutes to hours by raising themold temperature up to the cure temperature of the beads which dependson the curing agent used.

Depending on the desired final density of the ceramic component beingfabricated, the beads may be compressed to an apparent density of25%-98%

Additionally, if a non-porous, fully dense surface is desired, the spacebetween the semi solid spheres (beads) on and near the surface can beclosed off by applying extra beads and/or applying localized mechanicalpressure such that the surface beads are smeared, spackled or otherwiseforced into the open pores of the surface being sealed.

Once the green body is cured and pyrolyzed the resulting bulk ceramiccomponent will have a fully dense, non-porous surface suitable forpolishing, metalizing or any number of additional surface treatments.

An oven can be used that can be computer controlled. Such an oven caninclude but is not limited to a convection heated oven, microwave ovenor an oven using a combination of heat and electromagnetic radiation.Oven cure time can range from minutes to hours depending on cure agentused and cross sectional thickness of parts.

The processed green bodies can be fired in a furnace 60 to produce finalceramic components 70. The furnace can be an inert atmosphere furnacethat is computer controlled and capable of temperatures in theapproximately 800 C top approximately 1200 C range. The furnace can beoff the shelf retort type furnaces or custom built. Typical pryolysisschedules involve computer controlled ramp and soak functions that cantake the temperature from room temperature up to approximately 1000 C toapproximately 1200 C over several hours.

The resulting ceramic components can range in size from <1 mm to severalcm's and in theory is only limited by the size of the furnace. Gaspathways can make up from approximately 2% to approximately 98% of thevolume and can range in size from approximately 1 to approximately 50microns.

The term “approximately” can be +/−10% of the amount referenced.Additionally, preferred amounts and ranges can include the amounts andranges referenced without the prefix of being approximately.

Additionally, if a bulk ceramic component with complex internal featuresis desired such as a network of plumbing pathways for coolant flow, andthe like, the plumbing network could be fabricated out of a sacrificialmaterial that would decompose and be removed from the bulk part duringpyrolyzing.

FIG. 2 shows the steps of creating plumbing with bulk ceramiccomponents. The sacrificial material, in this example, could be polymertubing or rods that would be connected together in the desired patternand anchored to the mold so as not to move while the mold is beingfilled. The sacrificial material would be made to penetrate the surfaceof the molded part in at least one location so as to provide a gasescape pathway for the sacrificial material as it decomposes.

Step 1 is where the plumbing network is formed from sacrificial tubeshaped material. Step 2 is where the plumbing network is placed in amold.

After the plumbing network (as in this example) is created and placedinto a suitable mold, the remaining space in the mold would be filledwith the partially cured gelatinous beads as shown in Step 3.

After the application of suitable compression and/or vibration to themold in order to fully encase the plumbing network molding features. Themold can be placed in an oven to complete the cure with a resultinggreen body is formed inside the mold with the sacrificial plumbingnetwork embedded inside.

Once the molded part is fully cured, the green body would be removedfrom the mold and placed in a furnace for pyrolyzation in Step 5.

Upon pyrolyzation, the sacrificial plumbing network will have burned outleaving macroscopic passage ways (or any other internal feature desired)in the resulting bulk ceramic component. The Green body is placed in afurnace where the sacrificial plumbing network is burned off and thegreen body is converted to ceramic.

FIG. 3 shows the steps for creating conductor networks with bulk ceramiccomponents. As an additional example, if instead of a network ofplumbing for fluid flow, a network of electrical conductors can befabricated. One technique would be to form a network in the same manneras the fluid plumbing network, then, after pyrolyzing to a ceramic, theplumbing network could be filled with a molten metal conductor, thatupon solidifying would constitute an electrical conducting network.Steps 1, 2, 3, 4 and 5 shown in FIG. 3 shows steps similar to thosedescribed in FIG. 2.

Another technique to form an electrical conducting network would be tofabricate the network from insulated metallic conductors in a similarmanner to the plumbing network, then the conducting network would beplaced into a suitable mold, the remaining space in the mold would befilled with the partially cured beads.

After the application of suitable compression and/or vibration to themold in order to fully encase the conducting network molding features,the green body would be heated to complete the cure. During pyrolyzingthe insulation around the conductors would burn out thus creating roomfor the pyrolyzing beads to shrink around and capture the conductors.

The insulation material and thickness would be chosen such that it woulddecompose at a low temperature and provide the proper clearance betweenthe final ceramic body and the conductors. The conductor material wouldbe chosen such that it would be unaffected by the pyrolyzationtemperatures.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

We claim:
 1. A method of making pre-ceramic bulk parts with gaspathways, comprising the steps of: mixing liquid polymer precursors witha curing agent to form a mixture of liquid polymer ceramic precursorresins; spraying the mixture into droplets; partially curing thedroplets into a sticky and tacky state of particles; collecting thepartially cured particles; and molding the collected particles into ashaped pre-ceramic bulk part having gas pathways therethrough.
 2. Themethod of claim 1, wherein the particles are semi solid partially curedspheres that form gas pathways between them when they are pressedtogether.
 3. The method of claim 2, wherein the molding step includesthe step of: applying pressure to a collection of semi solid partiallycured sphere particles, wherein the size of the gas pathways are capableto be reduced to a selected level as long as the particles are notcompressed to the point where the space between them is reduced to zero.4. The method of claim 1, further comprising the step of: curing themolded collected particles with hot gas to produce a single continuouspolymeric part where the particles are indistinguishable.
 5. The methodof claim 1, further comprising the step of: curing the molded collectedparticles with radiation to produce a single continuous polymeric partwhere the particles are indistinguishable.
 6. The method of claim 1,further comprising the step of: producing the particles in a hot,non-reactive, immiscible, liquid bath via an emulsion process.
 7. Themethod of claim 1, further comprising the step of: co-spraying themixture of liquid polymer ceramic precursor resins with an inert fillerthat would burn out after curing the mixture.
 8. The method of claim 1,wherein the collecting step includes the step of: collecting thepartially cured droplets in one of a dry pan or a cooling bath.
 9. Themethod of claim 1, further comprising the steps of: creating anon-porous, fully dense surface on one or more of resulting green bodysurfaces, by closing off the space between semi solid spheres (beads) onand near the surface by applying extra beads and/or applying localizedmechanical pressure such that the surface beads are smeared, spackled orotherwise forced into the open pores of the surface being sealed; andcuring and pyrolizing the green body into a bulk ceramic component thathas a fully dense, non-porous surface; and treating the fully dense andnon-porous surface of the bulk ceramic component, wherein the step oftreating is selected from one of polishing, metalizing or an additionalsurface treatments.
 10. The method of claim 1, further comprising thestep of: varying ceramic porosity of the bulk part to be betweenapproximately 2% to approximately 98%.
 11. A method for producing bulkceramic components without using sponge materials to produce gaspathways in polymer bodies, comprising the steps of: mixing PDC (PolymerDerived Ceramics) resins in a chamber to form partially cured geldroplets; compressing the partially cured gel droplets into a resultingbody; coating the resulting body with a PDC resin; heating the PDC resincoated resulting body into a final state body; and firing the finalstate body in a furnace to produce a ceramic component having gaspathways there through.
 12. The method of claim 11, wherein the mixingstep includes the step of: mixing liquid PDC resins with surfactants andan inert liquid to form an emulsion of PDC resin droplets; and heatingthe emulsion to form the partially cured gel droplets.
 13. The method ofclaim 11, wherein the mixing step includes the steps of: spraying PDCresin into a curing chamber to form PDC resin droplets; curing the PDCresin droplets into the partially cured gel droplets.
 14. The method ofclaim 11, further comprising the step of: varying ceramic porosity ofthe ceramic component to be between approximately 2% to approximately98%.
 15. A method of converting plumbing networks into bulk ceramiccomponents, comprising the steps of: connecting together polymer tubingor polymer rods into a plumbing network; placing the plumbing networkinto a mold; packing the mold with partially cured gelatinous beads;curing the gelatinous beads in the mold to form a resultant solid greenbody inside the mold with the sacrificial plumbing network embeddedinside; removing the resultant solid green body from the mold andburning out the sacrificial plumbing network by pyrolyzation, whereinthe sacrificial plumbing network will have burned out leavingmacroscopic passage ways in a resulting bulk ceramic component whereasthe passageways provide a gas escape pathway for the sacrificialmaterial as it decomposes.
 16. The method of claim 15, wherein the stepof curing includes the step of: placing the mold with the partiallycured gelatinous beads in an oven; and forming a solid green body fromthe mold in an oven.
 17. The method of claim 15, wherein the step ofburning out includes the step of: placing the resultant green body withthe sacrificial plumbing network embedded inside in a furnace.
 18. Amethod of converting conductor networks into bulk ceramic components,comprising the steps of: forming a conductor network from conductivematerial having a sacrificial layer of insulation wrapped around theconductive material; placing the conductor network into a mold; packingthe mold with partially cured gelatinous beads; curing the gelatinousbeads in the mold to form a resultant solid green body inside the moldwith the conductor network embedded inside; removing the resultant solidgreen body from the mold; and burning out the sacrificial insulation onthe conductor network by pyrolyzation, wherein a sacrificial plumbingnetwork will have burned out leaving macroscopic passage ways; andforming a resulting bulk ceramic component whereas the passagewaysprovide a gas escape pathway for the sacrificial material as itdecomposes and the resulting ceramic component shrinks and captures theconductor material.
 19. The method of claim 18, wherein the step ofcuring includes the step of: placing the mold with the partially curedgelatinous beads in an oven; and forming a solid green body from themold in an oven.
 20. The method of claim 18, wherein the step of burningout includes the step of: placing the resultant green body with thesacrificial conductor network embedded inside in a furnace.